In order to insulate a surge arrester (also known as lightning arrester) from ground potential and thereby allow current measurements to be performed, the surge arrester is mounted on insulators. These insulators must in addition to a high insulation level also be mechanically strong since they are serving as foundation for the surge arrester. In the current design of such an insulator, two from each other separated threaded metal inserts are embedded in a moulded insulating material e.g. epoxy. The resulting mechanical strength is thereby limited by the moulded compound's adhesion strength to the respective inserts and by the tensile strength of the moulding compound itself. This presents a problem since the insulator may be subjected to significant and variable tensile stress over long periods of time, whereby the moulded material may crack.
The mechanical strength of the insulator may thus desirably be improved. Today the limiting factor is the moulding compounds adhesion to the inserts and the tensile strength of the moulding compound itself. It has been considered to increase the strength of the insulator by including supporting and strengthening electrically insulating material, such as glass fibre or ceramics in the moulded material.
GB 1,139,050 discloses an insulator for supporting overhead power lines, which is made by casting an epoxy resin body around a pre-stressed glass fibre loop, the tensile load on the loop being progressively reduced during curing of the resin so that the extension of the loop decreases at the same rate as the contraction of the resin, which may include plasticizers. The body may include an encapsulated strengthening member, e.g. a solid or tubular porcelain or glass fibre member.
GB 421,679 discloses an insulator comprising a body of insulating material and clamping bolts extending from two opposite faces of the body and overlapping or interleaving within the body such that a part of the body is held in compression between the heads of the bolts. The bolts and an annular clamping plate are positioned in and through the body after manufacture of said body. The insulator can be used for electrically conducting lines or rails.
U.S. Pat. No. 530,498 discloses a ball-shaped insulator where the insulated material is moulded around and between metallic parts comprising eye bolts.